Purpose: The association between physical function and
depressive symptoms has been widely discussed in literature.
However, the heterogeneity in measuring self-reported physical
function has obfuscated the applicability of research findings while
limited research investigated the association between performancebased
physical function and depressive symptoms. This study
aims to examine the association between both self-reported and
performance-based physical function and depressive symptoms.

Methods: Data were derived from the Population Study of
Chinese Elderly (PINE), a community-engaged, population-based
epidemiological study of U.S. Chinese older adults aged 60 and
above in the Greater Chicago area. Self-reported physical function
was measured by Katz activities of daily living (ADL), Lawton
instrumental activities of daily living (IADL), Index of Basic Physical
Activities scale and Index of Mobility scale. Performance-based
physical function was measured by Short Physical Performance
Battery (SPPB). Depressive symptoms and depression were assessed
by the Patient Health Questionnaire-9 (PHQ-9).

Discussion: This study initially examined the association
between both self-reported and performance-based physical function
and depressive symptoms and it further identified physical function
impairment was not only associated with depressive symptoms, but
also depression. Our study suggests that health professionals should
be aware of the depressive symptoms or depression in older adults
with physical function impairment.

Previous research reported physical function impairment had
a contemporaneous and strong effect on depressive symptoms
among a young and middle-aged population [1]. Understanding
the relationship between physical function and depressive
symptoms is particularly important for populations with high risk
of physical impairment, such as older adults [2]. Physical function
impairment is one of the most common features associated with
aging [3]. Many prior studies confirmed that depression is more
prevalent among disabled older adults [2].

The reciprocal relationship between physical function and
depressive symptoms has been well documented in literature
[4-6]. Existing studies indicated the effect of physical function
on depressive symptoms was faster and stronger than the
lagged effect of depressive symptoms on physical function [1,
2]. Some longitudinal studies found that prior levels of physical
impairment predicted changes in depressive symptoms, but
there was no evidence of the reverse association [7]. Depression
was also more reversible than physical impairment. Thus, this
study pays more attention to the association between physical
function and depressive symptoms.

Prior studies mainly focused on the association between
self-reported physical function and depressive symptoms, while
the association between performance-based physical function
and depressive symptoms has been understudied. Early studies
found lower levels of self-reported physical function, including
ADL, IADL, and physical functioning and mobility (PFM), were
associated with higher levels of depression among South African
older adults [8]. Studies also reported that increasing number
of self-reported physical impairment was associated with an
increased prevalence of depression in Latin American countries
[9].

As limited literature documented the association between
performance-based physical function and depressive symptoms,
this study aims to accumulate knowledge on the relationship
between both self-reported and performance-based physical
function and depressive symptoms in a largely communitydwelling
US Chinese old population. If the association between
physical function and depressive symptoms can be supported,
we’d like to go further to test whether physical function is
associated with depression.

Methods

Sample

The Population Study of Chinese Elderly in Chicago (PINE) is
a community-engaged, population-based epidemiological study
of U.S. Chinese older adults aged 60 and above in the Greater
Chicago area. The PINE study is a representative of the Chinese
aging population in the Greater Chicago area with a sample size
of 3,157 [10, 11]. Culturally appropriate community recruitment
strategies guided by community-based participatory research
(CBPR) approach were used to ensure community participation
[12-15]. Face-to-face home interviews were conducted by trained
multicultural and multilingual interviewers. Preferred language
(English or Chinese) and dialect (e.g., Cantonese, Taishanese,
Mandarin, and Teochew) for participants were used during the
interview. The study has been approved by the Institutional
Review Board of the Rush University Medical Center [16].

Measurements

Depressive Symptoms and Depression. Depressive
symptoms were measured by the Patient Health Questionnaire-9
(PHQ-9) [17]. Participants were asked if they had the following
symptoms in the last 2 weeks: (i) changes in sleep; (ii) changes
in appetite; (iii) fatigue; (iv) feelings of sadness or irritability; (v)
loss of interest in activities; (vi) inability to experience pleasure,
feelings of guilt or worthlessness; (vii) inability to concentrate or
making decisions; (viii) feeling restless or slowed down; and (ix)
suicide thoughts. The response on each item had four categories
ranging from 0 = not at all to 3 = nearly every day. Any “yes”
response was defined as having depressive symptoms. The total
score of PHQ-9 ranges from 0 to 27, with a score of 5 and more
indicating depression. The Cronbach’s alpha of PHQ-9 in the PINE
study was 0.82 [18, 19].

Confounding Variables. Socio-demographic factors were
controlled in data analysis, including age (in years), gender,
education, annual income, marital status, living arrangement,
number of children, years in the U.S. and medical comorbidities.
Education was categorized into three groups: (i) elementary
school and below; (ii) high school; and (iii) college and above. Selfreported
annual income was divided into three groups: (i) $0–
$4,999 per year; (ii) $5,000–$9,999 per year; and (iii) more than
$10,000 per year. Medical comorbidities were evaluated by the
presence of nine diseases: (i) heart disease, heart attack, coronary
thrombosis, coronary occlusion, or myocardial infarction; (ii)
stroke or brain hemorrhage; (iii) cancer, malignancy, or a tumor
of any type; (iv) high cholesterol; (v) diabetes, sugar in the urine,
or high blood sugar; (vi) high blood pressure; (vii) a broken or
fractured hip; (viii) thyroid disease; or (ix) osteoarthritis or
inflammation or problems with joints [26-28].

Data Analysis

Chi-square and t-test were used to compare the differences
in socio-demographics and physical function of older adults
with depressive symptoms and without depressive symptoms.
Chi-square and t-test were also applied to test the differences
in socio-demographics and physical function of older adults
with depression and without depression. Multivariate logistic
regression models were employed to test the association between
physical function and depressive symptoms/depression. Model A
was adjusted for age and gender. Model B added education, income
and marital status. Number of children, living arrangement
and years in the U.S. were added in Model C. Model D added
medical comorbidities to the previous model. In addition, all of
the above models (Models A–D) were repeatedly using physical
function with respect to depressive symptoms/depression
outcomes. Odds ratios (ORs), 95% confidence intervals (CIs), and
significance levels were reported for multivariate analyses. All
statistical analyses were conducted using SAS, Version 9.2 (SAS
Institute Inc., Cary, North Carolina).

Results

The older adults in the study sample had a mean age of 72.8
years (SD = 8.3, range = 60-105) and 58.9% were female. The
majority of participants (78.9%) had equal or less than a high
school education. Most of them (85.1%) had an annual income
less than US$10,000. 71.3% of participants were married, while
24.5% were widowed. More than half of the participants (55.6%)
averagely had 3 or more children. 21% of participants lived
alone. 26.7% of the participants had been in the United States for
less than 10 years. Details of the sample characteristics have been
described elsewhere [29, 36].

Table 3 showed ADL, IADL, Index of Mobility scale, Index of
Basic Physical Activities scale and physical performance testing
were significantly associated with depressive symptoms after
controlling for age, gender, education, income, marital status,
living arrangement, number of children, years in the U.S. and
medical comorbidities. As for self-reported physical function,
every one point higher in ADL impairment was associated
with higher risk of depressive symptoms (OR: 1.29, 1.14-1.45).
Greater levels of impairment in IADL were associated with
higher risk of depressive symptoms (OR: 1.17, 1.13-1.22). Every
one point higher in Index of Basic Physical Activities scale was
associated with higher risk of depressive symptoms (OR: 1.22,
1.19-1.26). Older adults with higher scores in Index of Mobility
scale were more likely to experience higher risk of depressive
symptoms (OR: 1.52, 1.39-1.66). With regard to performancebased
physical function, SPPB was significantly associated with
depressive symptoms (OR: 1.16, 1.12-1.19) after controlling for
all covariates. Specifically, every one point greater in tandem
stand (OR: 1.33, 1.22-1.44), timed walk (OR: 1.23, 1.16-1.30) and
chair stand (OR: 1.24, 1.18-1.31) was associated with higher risk
of depressive symptoms.

In Table 4, we tested the association between physical
function and depression. Consistently, both self-reported and
performance-based physical function was significantly associated
with depression. With respect to self-reported physical function
and depression, every one point higher in ADL (OR: 1.32, 1.21-
1.44), IADL (OR: 1.26, 1.21-1.31), Index of Basic Physical Activities
scale (OR: 1.24, 1.21-1.28) and Index of Mobility scale (OR: 1.85,
1.69-2.04) was associated with higher risk of depression. As for
performance-based physical function and depression, every one
point higher in SPPB (OR: 1.23, 1.19-1.27) was associated with
higher risk of depression. Every one point greater in tandem
stand (OR: 1.35, 1.25-1.46), timed walk (OR: 1.41, 1.30-1.53) and
chair stand (OR: 1.46, 1.36-1.57) was associated with higher risk
of depression.

This study found both self-reported and directly observed
physical function was significantly associated with depressive
symptoms after controlling for age, gender, education, income,
marital status, living arrangement, number of children, years in
the U.S. and medical comorbidities. In addition, both self-reported
and performance-based physical function was significantly
associated with depression.

Our study found self-reported physical function was
significantly associated with depressive symptoms. To be

specific, the present study confirmed that US Chinese older
adults with poorer report in ADL, IADL, Index of Basic Physical
Activities scale and Index of Mobility scale were more likely to be
associated with higher levels of depressive symptoms. Our results
were consistent with early studies conducted in South Africa and
Latin Americans that reported higher levels of impairment in
self-reported physical function were associated with higher risk
of depression [8, 9].

Our study goes beyond previous research by investigating
the association between performance-based physical function
and depressive symptoms. We found that US Chinese older
adults with poorer performance in SPPB were more likely to be
associated with higher risk of depressive symptoms. In addition,
each item in SPPB (i.e. tandem stand, walk and chair) was
significantly associated with depressive symptoms. Our study
enables the comparison between both self-reported and directly
observed physical function with depressive symptoms.

This study initially examined the association between both
self-reported and performance-based physical function and
depression. The results show higher scores in ADL, IADL, Index
of Basic Physical Activities scale, Index of Mobility scale and SPPB
were all significantly associated with higher levels of depression.
This result indicates physical function impairment was not only
associated with depressive symptoms, but also depression.
Physical impairment is a risk factor for the psychological wellbeing
of older adults.
These findings should be interpreted with cautions. First,
we didn’t use clinical diagnosis for depression. In our study,
depression was measured by PHQ-9, with a score of 5 and more
indicating depression. Second, although we tested the association
between physical function and depressive symptoms, the reverse
association may also exist. The mutual effects or causal effects
were difficult to be proved in a cross-sectional study.

This study has significant research implications. First, the
heterogeneity in measuring physical function has obfuscated
the applicability and comparability of research findings. Our
study provides insight into research on physical function and
depressive symptoms by using different measures of selfreported
and directly observed physical function. Second, this
study also allows the comparison between physical function and
both depressive symptoms and depression.

In policy practice, our study suggests health professionals
should be aware of the depressive symptoms or depression in
older adults with physical function impairment. We found various
kinds of physical impairment were significantly associated with
depressive symptoms and depression. Poorer report in ADL,
IADL, Index of Basic Physical Activities scale, Index of Mobility
scale and poorer performance in SPPB were associated with
higher risk of depressive symptoms and depression. Health
professionals are suggested to pay more attention on older adults
with physical impairment and conduct preventions for them
when needed.

In future research, the causal effects of self-reported and
performance-based physical function on depressive symptoms
may be strengthened by longitudinal research. Studies on testing
the combined effects of self-reported and performance-based
physical function on depressive symptoms are expected. Future
research can also examine the association between cognitive
impairment and depressive symptoms.

Conclusion

This study shows both self-reported and directly observed
physical function were significantly associated with depressive
symptoms after controlling for age, gender, education, income,
marital status, living arrangement, number of children, years in
the U.S. and medical comorbidities. The result for the association
between physical function and depression is consistent with the
association between physical function and depressive symptoms.
Future research may focus on the causal effects of self-reported
and performance-based physical function on depressive
symptoms.